Semiactive dampers are rapidly and repeatedly switched between high damping and low damping states in accordance with the dictates of a preselected control policy. One known control policy dictates that the damper be "on" or in a state of relatively high damping when the product of the relative velocity between the members interconnected by the damper, and thus "across" the damper itself, times the absolute velocity of the supported one of the aforesaid members, is greater than zero (i.e., is positive); and that the damper be in a low damping or "off" state when the aforesaid product equal to or less than zero (i.e., is negative or zero). Another known damper control policy dictates that the damper be in its relatively high damping or "on" state when the product of the relative velocity across it times the relative displacement between the sprung and unsprung members is less than zero (i.e., is negative or minus); and be in its relatively low damping or "off" state when the aforesaid product is greater than zero (i.e., when the sign is positive or plus). In optional modified versions of the aforesaid control policies, changes from one to the other of the damper states are deferred until the relative velocity across the damper is no greater than some preselected relatively low magnitude.
The foregoing and similar damper control policies may be and usually are implemented by electronic means which electronically monitors the conditions of motion of the damper and/or the members interconnected thereby, utilizes the monitored data (or data derived from it) to process the particular algorithm of the control policy, and then produces control signals that effect whatever change in the damping state of the damper as is dictated by the policy. The latter step usually is accomplished by the changing the position of an electrically or otherwise extraneously powered valve member that controls the flow of the hydraulic fluid of the damper. Under certain conditions of use, the power consumption, attendant heat generation, cost, efficiency and/or durability of semiactive dampers of the foregoing type may be unsatisfactory.
With the foregoing in mind, the primary object of the present invention is to provide an improved semiactive damper wherein significant monitoring and/or control functions are performed automatically by and more efficiently by hydro-mechanical means, rather than electrically.